1. Field of the Invention
The present invention relates to a liquid crystal panel, and more particularly to a liquid crystal panel device having a touch panel and a method for driving the same.
2. Discussion of the Related Art
A touch panel is a peripheral device of a computer, and can be loaded (or installed) on the display surface of a display device such as a cathode ray tube (CRT), a liquid crystal display (LCD), a field emission display (FED), a plasma display panel (PDP), an electric luminescence device (ELD). The touch panel allows a user to press the panel and provide input to the computer while watching the display surface of the display device.
FIG. 1 is a schematic view of a liquid crystal panel having a touch panel according to related art. The liquid crystal panel having a touch panel has a stacked layer structure. The liquid crystal panel 10 is located between an upper polarizing sheet 24 and a lower polarizing sheet 26, and the touch panel 12 is located on the upper polarizing sheet 24. According to the related art, the liquid crystal panel 10 includes an upper substrate, a lower substrate, and a liquid crystal material injected between the substrates and ball spacers for maintaining a space between the upper and lower substrates. The ball spacers also allow the liquid crystal material to have a uniform thickness.
The touch panel 12 includes an upper substrate 14 such as a polyethylene terephthalate (PET) film, a lower substrate 16, and spacers 22 distributed between the substrates. A first conductive layer 18 is formed on an under surface of the upper substrate 14, and a second conductive layer 20 is formed on an upper surface of the lower substrate 16. When the upper substrate 14 is pressed by a stylus pen or fingers, the first conductive layer 18 forms a short-circuit with the second conductive layer 20, thereby enabling generation of an electrical current or voltage level varying signal. The first and second conductive layers 18 and 20 are formed by printing silver Ag on a transparent conductive material such as Indium-Tin-Oxide (ITO), Indium-Zinc-Oxide (IZO) and Indium-Tin-Zinc-Oxide (ITZO).
This type of liquid crystal panel having a touch panel drives the liquid crystal in one of a dot inversion system, a column inversion system, and a line inversion system. Among these systems, the line inversion driving system is commonly used in small portable FDP's because of the reduced power consumption.
In the line inversion driving system, image data is applied to each line having alternating polarities of plus (+) and minus (−) opposite to a common voltage on a common electrode, thereby preventing the liquid crystal material from degradation.
FIG. 2 is a diagram of a driving apparatus for the liquid crystal panel having a touch panel as shown in FIG. 1 according to related art. In FIG. 2, the liquid crystal panel having a touch panel includes a liquid crystal panel 10, a touch panel 12, an analog-digital converter (ADC) 28 for converting a signal from the touch panel 12 into a digital signal, a central processing unit (CPU) 30 for producing signals of X/Y coordinates based on the digital signal, a transmission line 32 for transmitting the signals of the X/Y coordinates, and an application system 34 enabling a displaying content to be displayed on the liquid crystal panel based on the signals of the X/Y coordinates received from the transmission line 32. The ADC 28 and the CPU 30 form a touch controller. When a user touches the touch panel 12, the first conductive layer 18 and the second conductive layer 20 create a short-circuit such that an analog signal is generated having an electric current or voltage level. Subsequently, the analog signals X+, X−, Y+, and Y−, which were generated by the touch panel 12, each have the electric current or voltage level and are converted into the digital signals by the ADC 28.
Thereafter, the converted digital signals X+, X−, Y+, and Y− from the ADC 28 are input to the CPU 30 in a serial or parallel format. Then, the CPU 30 produces X and Y coordinates based on the converted digital signals X+, X−, Y+, and Y−. The signals of the X and Y coordinates generated from the CPU 30 are transmitted to the application system 34 through the transmission line 32. The transmission line 32 uses USB or PS/2 by applying a transmission protocol, such as RS 232. Finally, the application system 34 transmits a display controlling signal corresponding to the received X and Y coordinate signals to the liquid crystal module, thereby allowing a corresponding image to be displayed. In such a line inversion driving system, switching noise of a common voltage Vcom influences an arbitrary voltage value of the X/Y coordinate such that the output of the voltage value of the X/Y coordinate is unstable. Accordingly, an exact detection of the X/Y coordinates is impossible.
FIG. 3 is a waveform diagram of a liquid crystal driving voltage and a X/Y voltage signal of the touch panel of the liquid crystal panel shown in FIG. 1 according to the related art.
In FIG. 3, the voltages of X and Y include noises generated during a constant time interval due to rising and falling of the common voltage Vcom (i.e., a polarity reversal of the common voltage Vcom). Accordingly, when a user touches the touch panel using a stylus pen or a finger, a broad or trembling darkness problem occurs at the surroundings of the touched position because of noise. Thus, accurate detection of the coordinates is impossible.